A communication system can be seen as a facility that enables communication between two or more entities such as user equipment and/or other nodes associated with the system. The communication may comprise, for example, communication of voice, data, multimedia and so on. The communication system may be circuit switched or packet switched. Furthermore, there may be point-to-point, point-to-multipoint or multipoint-to-point connections. The communication system may be configured to provide wireless communication.
Block transmission refers to transmitting information bearing data in given blocks, where a block contains a fixed or a variable number of symbols or bits. Typically a whole block of symbols needs to be received before it is possible to detect reliably the symbols that were transmitted. In symbol-by-symbol transmission it is possible to detect a transmitted symbol based on a received symbol. Block transmission is used to mitigate effects due to inter-symbol interference (ISI) or, in case of code division, inter-chip interference (ICI) induced by a transmission channel. In transmitting digital data over frequency selective media, inter-symbol interference or inter-chip interference is a major performance limiting factor. Frequency selective media refers to certain frequencies exhibiting significant fading. Frequency selective fading becomes an issue especially for high transmission rates.
Block transmission using orthogonal frequency division multiplexing (OFDM) or code division multiplexing (CDM) waveforms has become popular in current communications systems and in proposals for future communications systems. ODFM is used, for example, in Digital Video Broadcasting—Terrestrial (DVB-T) systems and Wireless Fidelity (WiFi) systems, for example those that meet the IEEE 802.11 specifications. ODFM has also been considered for various future wireless systems. Multicode (CDM) transmission is used in 3G cellular systems, for example in Wideband CDMA (WCDMA) and cdma2000 systems. In addition, various combinations of the above have been proposed, for example multi-carrier CDMA systems which contain frequency-spreading (or preceding) before transmitting the symbols via a subcarrier or subcarriers.
Both of OFDM and CDM systems have their advantages and drawbacks. OFDM has a high peak-to-average power ratio (PAR). PAR results from simultaneous (parallel) transmission of several sub-carriers, and the peak power typically increases as the number of (simultaneously transmitted) summed carriers increases. High PAR typically requires an expensive or complex amplifier and therefore it is of interest to define signaling so that PAR is reduced as much as possible. Furthermore, there are tradeoffs in performance. Namely, due to lack of diversity, the performance of OFDM saturates whenever the outer coding rate is high (above ¾ say). On the other hand, an OFDM receiver is simple, as OFDM signals can be optimally detected with operations involving Discrete Fourier Transform (DFT) or Fast Fourier Transform (FFT). This optimal detection assumes the use of cyclic prefix, zero padding or other relevant guarding between transmission blocks. Furthermore, the transmission channels should be perfectly estimated. On the other hand, CDM or combined CDMA-OFDM distributes symbol energy over multiple frequency bins increasing frequency diversity. CDM therefore often has better performance than OFDM, provided that a proper and a more complex receiver is used.
A chip-interleaved, block-spread multiuser communications method and system has been discussed by S. Zhou, G. B. Giannakis, and C. Le Martret, in “Chip-Interleaved Block-Spread Code Division Multiple Access”, IEEE Transactions on Communications, Vol. 50, No. 2, February 2002. There exists also a relating U.S. patent application 2002/0126740. The chip-interleaved block-spread code division multiple access (CIBS-CDMA) transmission may be implemented by processing symbols to be transmitted in accordance with code division, that is by spreading each symbol with a spreading code consisting of chips. The resulting chips may then be written into a buffer row by row, each row containing chips of a symbol. After chips relating to a set of symbols (block) have been written to the buffer, zero padding (a row of guard chips) is added for avoiding interference between sequential chips relating to a given symbol. The chips are then read out from the buffer column by column.
An aim of the present invention is to provide a versatile method for block transmission.